1. Field of the Invention
This invention relates to vehicle axle assemblies in general, and more particularly, to an axle disconnect assembly for an auxiliary drive axle assembly of a four-wheel drive motor vehicle.
2. Description of the Prior Art
Four-wheel drive vehicles which are operable in either a two-wheel drive mode or a four-wheel drive mode are known as part time four wheel drive vehicles, are well known in the prior art. It is also known to provide the part time four wheel drive vehicle with an axle disconnect (or differential disconnect) mechanism in a front (or sometimes rear) axle assembly. Various axle disconnect assemblies or mechanisms have been proposed. These mechanisms in general have a number of moving parts, are fairly complex, and would be suitable only for installation on relatively wide vehicles because of the space required.
Such axle disconnect mechanisms typically include a fluid motor (hydraulic, pneumatic or vacuum) and a shift fork assembly. The fluid motor communicates with a fluid source that is usually controlled by a two position solenoid valve. The fork shift assembly under control of the fluid motor controls the axial shifting of a clutch collar between positions corresponding to coupled and uncoupled operating modes.
This conventional system has the drawback of an externally mounted actuator that requires considerable extra space particularly when vehicle suspension travel is taken into account. The use of an externally mounted actuator also necessitates the use of a fork shift assembly which adds to the cost and complexity of the prior art arrangement exemplified by this system. Moreover, such prior art axle disconnect systems do not provide a modular arrangement necessary for easy of manufacture, assembly and repair. Consequently these prior art arrangements are also complex and expensive to produce particularly when the difficulty of assembly is taken into account.
Moreover, the prior art axle designs typically include an axle shaft with male splines connected to a side gear bore with female splines, to prevent relative rotation and transmit torque. For beam axles (or rigid axles), shaft lateral movement is usually restrained by (A) the shaft bearing at the wheel end, or (B) a C-clip attached to the axle shaft inboard of the side gear. For independent axles, i.e. the axles allowing the relative motion (or travel) between the left-hand and right-hand outer axle shafts, the shaft lateral movement is usually restrained by a collapsing/expanding ring contained within grooves on the shaft O.D. and side gear bore I.D.; this method is utilized for independent axles to facilitate shaft connection to the axle during the vehicle build. To integrate axle disconnect mechanisms within an independent axle assembly, the prior art methodology of axle shaft retention is not satisfactory. C-clips and expanding rings cannot be used because the shaft and side gear must be capable of rotating independently in disconnect mode. The shaft cannot be retained exclusively at the wheelend, because the length of the shaft varies due to wheel travel and the inboard plunging CV joint. Therefore, a new mechanism is required to (A) retain the shaft within the axle assembly, and (B) permit shaft to side gear relative rotation.
The need therefore exists for an axle disconnect assembly and an axle shaft retention in an independent axle assembly that are simple in design, compact in construction and economical to package and manufacture.